Question

The freezing point of a solution prepared by dissolving 150 × 10–3 g of caffeine in 10.0 g of camphor is lower by 3.07°C than that of pure camphor (Kf = 39.7°C/m). What is the molar mass of caffeine?

Answer 1

Molar Mass=193.9738 g/mol

Molar Mass≅194g/mol

Step-by-step explanation:

Consider the formula:

m=ΔT/K_{f}

where:

ΔT is freezing point depression

K_{f} is freezing point depression constant

m is the morality=(moles of solute/kg of solvent)

Now:

`m=(3.07)/(39.7)`

`m=0.07733 moles of solute/kg of solvent`

Now:

0.07733 (moles of solute/kg of solvent) *0.010 kg of solvent

`7.733*10^(-4)` moles of solute(Caffeine)

Molar mass = Mass of solute/moles of solute

Molar Mass=
`(150*10^-3)/(7.733*10^(-4) )`

Molar Mass=193.9738 g/mol

Molar Mass≅194g/mol